I like tip up with the knife near the back seam of my front pocket. A good strong clip will keep the knife in position so the blade has nowhere to open while in the pocket. YMMV.
X2 Ball detents that most folders have and any lockback will keep the blade closed as well. I carry tip-up because I've found that its simply more natural; its like drawing a knife from a sheath. Furthermore, when one inserts the thumb in to grasp the knife its already positioned near the stud/hole/button: no changing grips. You can't use a wave tip down either
